Integrated Numerical Modeling of Heat Transfer, Hydrocarbon Formation, and Migration in Two Dimensions: The Themis Model

P. Ungerer, B. Doligez, F. Bessis, J. Burrus, P. Y. Chenet

The Themis Basin Model is an operational tool devised at the Institut Francaise du Petrole (IFP) for practical cases of oil exploration. From already tested mathematical equations, it reconstructs the history of heat transfer, compaction, hydrocarbon formation, and migration. Compared to previous models, it permits a more realistic description of sedimentation. The two-dimensional mesh used to solve the various equations is evolutive and accounts for possible nondepositions, pinch-outs, truncations, paleobathymetry, eustatic changes, and contrasting lithologies.

This mesh applies not only to the sediments but also, if necessary, to the whole sediment-crust-mantle system. Conductive heat transfer as well as regional hydrodynamics are taken into account in the sediments, and conduction only in the basement. The model can represent crustal and mantle thinning as well as radioactive heat production in the upper crust and in the sediments.

For practical applications, the model is organized in several modules that may be processed either separately or together, depending on the kind of data available. In the preliminary exploration of a basin, only temperatures and maturation are computed, assuming compaction is normal. This points out the zones where possible source rocks, if present, are mature. In later stages, when source rocks are better known, a global mass balance of oil and gas formation may be derived from the model. Finally, compaction may be reconstructed, assuming either monophasic fluid flow (history of pore pressure) or biphasic flow (hydrocarbon migration), integrated with temperature reconstruction.

The main results of the model, such as temperature, pressure, porosity, maturity, and hydrocarbon saturation, are automatically plotted in the form of successive cross sections or as evolution curves through geologic time.

Several examples of real basins, including the North Sea Viking graben, the Western Mediterranean margin, and the Suez rift are presented, illustrating the various applications of the Themis Model and showing how this approach can increase the efficiency of oil exploration.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.